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common-mode??


mudball
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Hi Mudhall,
Welcome to our forum. ;D
Common-mode signals to an opamp are signals that are the same at both inputs. The range of common mode signals for most opamps is within a few volts from each supply voltage. A few opamps like the LM324 and LM358 have inputs with a common mode voltage range that includes the negative supply, which sometimes is the circuit's ground. A feww opamps have an input common mode range that includes the positive supply voltage. New Cmos opamps have an input common mode voltage range that includes all its voltages and are called input rail-to-rail.

An opamp is supposed to have differential inputs and therefore amplify only the difference between its inputs, but the inputs are not perfect and amplify common mode signals a little, and more at higher frequencies. The amount of rejection is called input common mode rejection.

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Hi Mudhall,
Welcome to our forum. ;D
Common-mode signals to an opamp are signals that are the same at both inputs. The range of common mode signals for most opamps is within a few volts from each supply voltage. A few opamps like the LM324 and LM358 have inputs with a common mode voltage range that includes the negative supply, which sometimes is the circuit's ground. A feww opamps have an input common mode range that includes the positive supply voltage. New Cmos opamps have an input common mode voltage range that includes all its voltages and are called input rail-to-rail.

An opamp is supposed to have differential inputs and therefore amplify only the difference between its inputs, but the inputs are not perfect and amplify common mode signals a little, and more at higher frequencies. The amount of rejection is called input common mode rejection.

Great explanation, AG!
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